Introducing reduced data set information into a primary image data set

ABSTRACT

Secondary data set information is incorporated into a primary data set (such as a digital image) retaining a desired dynamic range and retaining the original primary set data quality. The secondary data set information is `smuggled` into the least significant bits of the primary data set to result in an enhanced data set. If desired, the primary data word can be shifted toward the most significant bit. The enhanced data set may be viewed as if it were the original primary data set with existing playback devices, however it now includes additional `smuggled` information which may be played back in coordination with the primary data set information. One example is flow-direction information `smuggled` into an angiographic image. The least significant bits of the enhanced data words may be used to select the color map and color code the images. A user-adjustable intensity threshold can also be employed to select between color maps. Information stored in this fashion results in a substantial savings in disk storage requirements. Also, since the information of the primary and secondary data sets are merged into a single word, they will remain together throughout many different types of processing, such as maximum intensity projection in volumetric imaging.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to data compression and playback.

2. Discussion of Prior Art

Related data sets may be closely linked such that it is desirable toplay back both simultaneously. Several volumetric data sets measuringdifferent physical parameters sampled at substantially the samelocations can exist. For example, in meteorological data this may bewind velocity and temperature of a given volume.

This may also apply to several volumetric data sets acquired by amedical imaging device of the same volume of a subject. For example, inultrasonic imaging, a Doppler shift data set in the detected ultrasonicfrequency signal may be used to quantify blood speed and direction offlow in addition to the standard imaging data set.

In Magnetic Resonance Imaging, thermal and velocity data sets may beused in addition to the standard MR image data set, the additionalinformation being played back in imaging by color coding on an otherwisegray-scale image. Color coded overlays have been used to show thermalhot-spots in phase-sensitive temperature imaging. Color coded overlayshave also been used to highlight areas of activation in functional brainMRI scans.

One challenge with existing methods of playback is that the data setcontaining the additional information is sometimes as large (or larger)than the primary data set. This can greatly overload the disk capacityand data-transfer bandwidth of a scanner.

Playback of processed data is also difficult since much information maybe lost during processing. For example, in MR imaging playback, it isfrequently convenient to reduce a three-dimensional data set into atwo-dimensional projection image. This is often done using a MaximumIntensity Projection (MIP). Current methods for the generation of MIPimages from three-dimensional phase contrast angiograms are applied tothe magnitude component of the data, thereby losing all directionalinformation. MIP data from the quantitative velocity data could beperformed, but the MIP would have to be performed three times (one foreach flow component) over the three-dimensional data set to provide afull analysis.

Currently, there is a need for a system which incorporates additionalinformation in primary data sets allowing display of more than oneparameter simultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention believed to be novel are set forth withparticularity in the appended claims. The invention itself, however,both as to organization and method of operation, together with furtherobjects and advantages thereof, may be best understood by reference tothe following description taken in conjunction with the accompanyingdrawing in which:

FIG. 1 is a simplified block diagram of a method for incorporating phaseinformation from a phase-sensitive MR data acquisition into magnitudedata from the same acquisition.

FIG. 2 is a simplified block diagram of a method for incorporatingactivation information from a functional MR data acquisition intomagnitude data from the same acquisition.

FIG. 3 is a representation of a conventional display word representing asingle pixel used in a conventional black and white images and onemodified according to the present invention.

FIG. 4 is a representation of a conventional color mapping used in thedisplay of image data.

FIG. 5 is a representation of a first embodiment of color mapping ofdisplay words with `smuggled` bits according to the present invention.

FIG. 6 is a representation of a second embodiment of color mapping ofdisplay words with `smuggled` bits according to the present invention.

FIG. 7 is a representation of a third embodiment of color mapping ofdisplay words with `smuggled` bits according to the present invention.

FIG. 8 is a simplified block diagram of one embodiment of the presentinvention for creating and displaying enhanced image data.

FIG. 9 is a simplified block diagram of a second embodiment of thepresent invention for creating and playing back enhanced data sets.

SUMMARY OF THE INVENTION

There is a need to store additional information in primary data sets forlater enhanced playback. This may be applied to imaging showing regionsof activation in functional MRI images, and flow-direction informationin MR angiograms without, increasing the size of the stored data.

To be useful, the enhanced data set should be compatible with existingdisplay methods, such as filming and direct viewing on a gray-scalemonitor and data reduction schemes (such as MIP).

In the present invention, primary data words are mathematically alteredto `smuggle` in additional information from a secondary data set. Thisadditional information is then used to enhance the playback of theenhanced data set. An example would be changing the pixel color and/orintensity of a display to illustrate selected features and/or aspects ofa digital image.

The least significant bits of the digital words in the pixels of theenhanced data set are used to store the additional information. This isaccomplished by shifting the digital words of the primary data set by aselected number of bits, thereby vacating the least significant bits.For example, if three bits of additional information are desired, theneach pixel in the digital image would be multiplied by 2³ =8. Althoughthe dynamic range of the image data is reduced by three bits, inpractice this will rarely present a problem since most images do notmake full use of their dynamic range (typically 16-bits or 32-bits).

When the dynamic range of the image encompasses the full word size,however, an alternate embodiment of the present invention in which theleast significant bits of the original image data are replaced with theadditional information bits can be employed.

One use of the present invention is in Phase-contrast Magnetic ResonanceAngiography (MRA). Here, the direction of blood flow may be incorporatedas additional information in the digital display word.

Once the additional information is `smuggled` into the data as part ofthe acquisition process, an operator may later examine the enhanced dataset during playback. In imaging, if the operator uses conventionalfilming functions or views the data on a gray-scale display (such as thescanner console) then the enhanced images will appear as normalgray-scale images. If the operator desires, however, the bits may beused to control the color of the viewed pixels.

If the `smuggled` bits are used to colorize data, then regions of theimage containing noise will also be colorized. This may present anundesirable display. To avoid this problem, a control similar to thoseused for window and leveling of gray-scale data can be used to specify athreshold for the application of the color look-up table. For example,if this threshold is relatively high, then only intense pixels will becolorized. If the threshold is relatively low, then more pixels will becolorized.

One significant advantage of colorizing data with additional informationwhich has been `smuggled` into the original image data is that the datacan be processed by Maximum Intensity Projection (MIP) algorithmsmethods without loss of the `smuggled` bits since they are now part ofthe display word. Consequently, a two-dimensional projection can bemanipulated and colorized as easily as the source three-dimensionalimage.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a system whichcombines digital information from two or more independent sources into asingle image to reduce data storage requirements.

It is another object of the present invention to provide a system forthe display of image data containing information from two or moreindependent sources.

It is another object of the present invention to provide color coding ofmagnetic resonance angiograms.

It is another object of the present invention to provide color coding offunctional magnetic resonance images.

It is another object of the present invention to combine informationacquired with multiple imaging modalities.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention information from two or more data sets arecombined into a single enhanced data set in which one component ofinformation is placed in the most-significant bits of the pixel displayword and the other components of information are placed in theleast-significant bits of the enhanced data words. Since the additionalcomponents of information are placed in bit locations which are lesssignificant than the lowest bits of the first component of information,the combined data set can be manipulated and displayed with conventionalmeans. The additional information, however, can be used in manipulationsand/or displays if desired.

FIG. 1 illustrates a first embodiment of the present invention in whichPhase-Contrast Magnetic Resonance Angiography (PC-MRA) data isprocessed. Phase-Contrast Magnetic Resonance Angiography data consistsof two components of information. The first component is contained inthe magnitude of the acquired MR signal and reflects the strength of theMR signal. The second component is contained in the phase of theacquired MR signal and reflects the velocity of the material giving theMR signal.

In phase-contrast MRA up to three orthogonal flow-sensitive acquisitionsare performed in each slice of the subject. Consequently, athree-dimensional Phase Contrast (3DPC) angiogram consists of up to fourdifferent three-dimensional data sets after image reconstruction. Thesedata sets are: 1) magnitude data, 2) X-flow, 3) Y-flow and 4) Z-flow.Each of the flow data sets consists of a magnitude component whichreflects the signal intensity of the moving blood, and a phase componentwhich reflects the blood's velocity. Using one embodiment of the presentinvention, the X-flow, Y-flow and Z-flow velocity data can each bereduced to a single bit giving the direction of flow (e.g. 0=left,1=right). These three bits of information can then be inserted as theleast significant bits of the magnitude data set to give an enhanceddata set.

In FIG. 1, an X-flow sensitive image containing a magnitude component110a and a phase component 110b, a Y-flow sensitive image containing amagnitude component 120a and a phase component 120b and a Z-flowsensitive image containing a magnitude component 130a and a phasecomponent 130b are treated with the system of the present invention. Itis instructive to note that the present invention can be applied to alltypes of PC-MRA data including two- and three-dimensional data sets.

In the present embodiment of the invention, X-flow phase component 110b,Y-flow phase component 120b and Z-flow phase component 130b are eachreduced to a single bit of information for each pixel. One usefulreduction method is to extract the sign of the phase components in orderto obtain a single data bit for each of the X, Y and Z-flow images tocharacterize the direction of flow. For example, if the phase of the Zcomponent data is positive, that would indicate that the direction offlow was in the positive Z direction and thus, the Z bit would be set(i.e. =1). Conversely, if the flow was in the negative Z direction, thenthe phase of the Z component would be negative and the Z bit would notbe set (i.e. =0). Reduction of the X-flow data is accomplished with an Xphase reduction step 140a, reduction of the Y-flow data is accomplishedwith a Y phase reduction step 140b and reduction of the Z-flow data isaccomplished with a Z phase reduction step 140c. The individual bits arethen combined into a single three bit word using a bit combine step 160.

In the present embodiment the magnitude components of the X-flow, Y-flowand Z-flow images are combined in a magnitude combine step 150. In thepresently preferred embodiment the magnitude components are combined ina fashion well know to those skilled in the art using the equation:

    Combined magnitude=square root of (X.sup.2 +Y.sup.2 +Z.sup.2)(1)

Where X, Y and Z are the magnitude of the X-flow, Y-flow and Z-flowimage data respectively.

Once the X, Y and Z magnitude components have been combined, theresultant image data has pixel intensities which reflect the speed offlow within the imaged vessels, but does not contain any informationregarding the direction of flow. Conversely, the three bit word computedin combine step 160 contains direction of flow information, but does notcontain any information regarding the strength of the MR signal. In thepresent invention, the three bit word computed in combine step 160 isinserted into the least-significant bit locations of the combinedmagnitude component determined in magnitude combine step 150. Thisinsertion is performed in an insertion step 170. If desired the combinedmagnitude data can be shifted into the more significant bit locationsprior to the insertion of the three bit word. This preserves the entireimage content provided there is sufficient dynamic range in the originalmagnitude data.

Alternatively, the three least significant bits of the combinedmagnitude data can be replaced with the three bit word. This alters thefine intensity structure of the image (i.e. noise), but preserves thedynamic range.

A second embodiment of the present invention is illustrated in FIG. 2 inwhich data from a Functional Magnetic Resonance Imaging (fMRI) data isprocessed. In this embodiment, a reference scan 210 is first acquired. Aplurality of n subsequent images 220a, 220b, 220c . . . 220n, are thenacquired. The magnitude of pixels in each subsequent image 220a, 220b,220c . . . 220n are then subtracted from the magnitude of correspondingpixels in reference image 210 using a subtraction step 230. The resultof each subtraction is then reduced to a selected number, M, bits ofdata in a difference reduction step 240. In one embodiment thedifference data are scaled so that all possible values lie between-(2^(M-1) -1) to 2^(M-1). In an alternate embodiment, the sign of thedifference is assumed to be positive and the difference data is scaledso that all possible values lie between 0 and 2^(M) -1.

Once the reduced data has been computed, it is inserted into the leastsignificant bits of the reference image using a bit insertion step 250.As with the first preferred embodiment, the reference pixel data can beshifted into the more significant bits prior to insertion of the reduceddata, or if desired, the reduced data can replace the least significantbits of the reference image.

It should be noted that the second embodiment of the present inventionalso has application to any digital imaging method in which a referenceimage is acquired and compared to subsequent images. These applicationsinclude, but are not limited to: temperature sensitive MR imaging, MRspectroscopic imaging, digital x-ray angiography and highlightingdifferences in satellite images.

FIG. 3 illustrates a data word 300 of a single pixel in a conventionaldigital image. In this example, 32 bits are contained in the pixel andeach bit has either the numeric value 0 or 1. Data word 300 has amost-significant bit 310, a least-significant bit 320 and a fourthmost-significant bit 330.

Enhanced data word 350 is data word 300 after being modified accordingto the present invention. Enhanced data word 350 has a most significantbit 360. Additional information 390 is inserted below aleast-significant bit 370 of enhanced data word 350. In thisillustration, additional information 390 is comprised of three bits380a, 380b and 380c. This three bit insertion is consistent with use ofthe first embodiment of the invention in which three orthogonal flowdirections are inserted into the data. This three bit insertion is alsoconsistent with the use of the second embodiment in which M=3.

Least significant bit 370 corresponds to the original least significantbit of the unaltered data 320 of data word 300 and most significant bit360 corresponds to the fourth most significant bit 330 of data word 300.

FIG. 4 illustrates the conventional process in which pixel data in animage is converted into intensities for display on a color monitor, inthis example, a 16 bit dynamic range for each display word resulting invalues between -32,768 and 32,767. Since the full dynamic range of theimage data greatly exceeds that of the human eye, a subset of the fullrange of the data is chosen by the operator. This subset is specified bytwo parameters, a window, W, and a level, L.

Window W specifies the range of pixel intensity values which are passedto the display hardware. Level L specifies the average pixel intensityvalue passed to the display hardware. In conventional display systems,the pixel intensities specified by W and L are scaled and interpolatedto give numeric display intensity values 420 which for an 8 bit displayhas values between 0 and 255. Pixels whose values exceed the upper boundof the subset are given a display value of 255 and pixels whose valuesare less than the lower bound of the subset are given a display value of0. In practice the operator can easily manipulate W and L (typicallywith knobs) and rapidly adjust the contrast and brightness of thedisplayed image to optimize the visualization of any part of the image.

If the final display driver is designed to drive a black-and-whitemonitor, then display intensity values 420 are directly sent to thedigital-to-analog converters (DACs) which in turn provide the intensitydrive voltages to the monitor.

For color monitors, display intensity values 420 are typically passed toa color look-up table 430 which converts each display intensity valueinto display intensity values for the red, green and blue drivers of thedisplay. If a gray scale image is displayed using color look-up table430, then the numeric outputs of the red, green and blue drives areequal to each other and vary from 0 to 255. When red, green and blue areall 0, then the monitor displays black. When red, green and blue are all255 then the monitor displays white. Intermediate values giveintermediate levels of gray.

In the present invention, the additional data which has been insertedinto the original data is not viewable using conventional image displaysystems. Consequently, one aspect of the current invention is alternatedisplay mechanisms which can make use of the inserted data. A firstexample of this is shown in FIG. 5. Here a pixel datum 411 is analyzedin the conventional fashion for a given window W and level L, to give adisplay intensity value 421. In accordance with the present invention,however, one of the bits contained in the additional information (390 ofFIG. 3) becomes a control bit and is used to select between two colorlook up tables. If the control bit is set (i.e. =1), then a first colorlook-up table 431 is selected. If the control bit is not set (i.e. =0)then a second color look-up table 441 is selected. In an additionalaspect of the present invention, each color look-up table can bedynamically modified by the operator through the specification of acolor threshold 451. In the present example, color look-up values belowthe threshold, shown as value A in FIG. 5, are set to give an imageappearance identical to a conventional black and white image. Colorlook-up table values above the color threshold are modified to give acolorized image.

With the example given in FIG. 5, phase-contrast MRA data obtained inaccordance with the first embodiment of the present invention wouldappear as a conventional black-and-white image when the color threshold451 is maximized (i.e. A=255). As the threshold is lowered, however,pixels whose magnitudes have a display value greater than A will bedisplayed with a colorized look-up table.

In the example shown in FIG. 5, those pixels whose control bit is setwill be given a red hue since the green and blue components are zeroed.Alternatively, those pixels whose control bit is not set will be given ablue hue. With phase-contrast angiography data, vessels carrying bloodin a selected direction will appear red while vessels carrying blood inthe opposite direction will appear blue.

FIG. 6 shows an alternative color mapping scheme in which a pixel datum412 is reduced to a display intensity value 422 which in turn driveseither a first color look-up table 432, or a gray scale-lookup table 442depending on the status of a selected control bit. A color threshold 452is applied to first color look-up table 432 as described above, but notto second color look-up table 442. Consequently, when pixel display wordintensities are above the color threshold value, A, they are colorizedonly if the control bit is set. With phase-contrast angiography data,vessels carrying blood in a selected direction will appear red whilevessels carrying blood in the opposite direction will appear with theconventional black-and-white appearance.

In the embodiments of the present invention disclosed in FIGS. 5 and 6,a single control bit is used to select the color look-up table. Inalternate embodiments, M bits can be used to select between 2^(M) lookuptables as shown for M=4 in FIG. 7. In this embodiment of the invention apixel datum 413 is reduced to a display intensity value 423 which inturn drives one of sixteen color look-up tables 433a, 433b, 433c . . .433p. The selection of the color look-up table determined by the value,B, of the M=4 control bits. A color threshold 453 is applied to eachcolor look-up table 433 as described above, but not to last colorlook-up table 433p.

Thus, functional MRI data acquired and reduced in accordance with thesecond embodiment of the present invention in which M=4, are displayedwith 16 different color look-up tables. Pixels in the image having nochanges with respect to the reference image (i.e. no functionalactivation) have a zero stored as the additional information (i.e. B=0)which causes the display to select a conventional black-and-whitelook-up table 433p. Image pixels having moderate changes would cause thedisplay to select a `cool` hue such as blue for its look-up table. Imagepixels having greater changes would cause the display to select anintermediate hue such as green for its look-up table 433c. Image pixelswith large changes would cause the display to select a `hot` hue such asred for its look-up table 433a. As with the embodiments illustrated inFIGS. 5 and 6, a color threshold allows the user to dynamically selectthe amount of colorizing applied to the displayed image.

With the present invention, any colorized look-up table is possible.With the illustrated embodiments the operator has the impression thatselected image pixels are viewed through colored glass (i.e. the detailsof the underlying source image are still apparent). The hue of thecolored glass (e.g. red, green, blue etc.) is determined by the controlbits which contain additional information (e.g. flow direction, degreeof functional activation etc.). In our previous example, the if theoperator wishes to determine the direction of flow in the left/rightaxis, then the value of the bit in the position corresponding to thereduced left/right velocity information can be used to select betweentwo alternative color look-up tables. Pixel data with the `left/right`bit set could be represented with a red-to-black color table while pixeldata with the `left/right` bit not set could be represented with ablue-to-black color table. Alternatively, if display of only flow in asingle direction is desired, then the color-to-black lookup table can beapplied for only those pixels having the appropriate inserted bit value,and a conventional white-to-black look-up table used for all otherpixels.

The use of a color threshold permits the colorization of only relevantpixels and leaves the non-relevant pixels (e.g. noise background outsidethe imaged anatomy) displayed in black and white.

FIG. 8 illustrates one embodiment of a hardware system 500 for theincorporation of additional image data into a primary digital imagewhich may be displayed as the primary image with little change indynamic range or visible appearance, or may be displayed as an enhancedimage, with color coding or overlays. A computer bus 501 connects a diskstorage means 510, a Central Processor Unit (CPU) 520, and a memorymeans 530, to a graphic display subsystem 540, and acts as a source ofprimary data.

Graphic display subsystem 540 is comprised of a memory buffer 550, acontrol device 555, and a color look-up device 560. Color look-up device560 is connected to user input devices comprised of a window control580a, a level control 580b and a color threshold control 580c.

In accordance with the present invention CPU 520 acquires a primary dataset, which may be in memory 530 or stored on disk storage device 510,and inserts it into a working memory buffer 550 via a merge device 553.

A data reduction device 557 either has pre-stored, or receives asuser-defined, a desired dynamic range required for playback, indicatinga number of playback bits D. It also has pre-stored, or is user-suppliedwith, the word width of the playback device P intended to be used. Fromthis data reduction, device 553 determines the amount of free bits, F,which may be merged into the primary data set words.

Data reduction device 557 is coupled to a secondary data source 551. Thesecondary data source 551 may physically be the same acquisitionequipment used to acquire the primary data set, but produces a secondarydata set. Data reduction device 557 reduces the secondary data wordsdown to reduced secondary data words each having M bits.

Data reduction device 557 in certain circumstances determines anappropriate length for M, such as when the secondary data may be reducedto a fixed number of bits. For example, flow direction data may bedefined in three bits with each bit indicating a direction along threeorthogonal directions.

Merge device 553 is coupled to the data reduction device 557 andreceives the M least signicant bits of the primary data word and the Mbits of each secondary data word. It also receives information from thedata reduction device 557. Merge device is also coupled to memory buffer550 and shifts each primary data word M bit positions toward the mostsignificant bit, and inserts the M bits of the reduced secondary dataword into the M least significant bit positions.

In the event that F was determined to be less M, then the merge device553 shifts the primary data word by F bits and inserts M bits of thereduced secondary data word into the lowest M bits of the primary dataword. The merged primary and secondary data word information results ina new enhanced data set with enhanced data words of the same width asthe primary data set words.

The enhanced data words have the secondary data information merged intothe lowest bits. This will only minimally affect the values, especiallyif M is chosen to be about or below the number of bits equivalent to thelevel of background noise. This allows the enhanced data sets to bedisplayed as if they were unaltered primary data sets on conventionalplayback equipment. For example, enhanced color coded MR angiographydata may be displayed as original gray scale information on conventionalgray scale MR Scanners with little or no change in dynamic range, imagequality, or storage space. These same enhanced data sets may also beviewed as color coded images on an enhanced MR Scanner employing thepresent invention.

On playback, CPU 520 places the enhanced digital image into displaymemory buffer 550.

Color lookup device 560 receives the window, level, and color thresholdinformation from the window, level and color threshold control devices580a, 580b, 580c, respectively. It then creates at least one colorlookup table with the entries above the color threshold shades of apredetermined color or colors. Entries at, and below, the colorthreshold define shades of gray scale. Each entry has an index. Thetable is constructed such that the window range maps into indices of thelookup table and spans all indices of the table.

A control device 555 reads the additional information stored in the Mleast significant bits of the enhanced data word and acts accordingly.

In color coding of digital images, the additional data indicates whichlookup table within color lookup device 560 to use.

Color lookup device 560 then provides the extracted color or gray scaleto Digital-to-Analog converters 571 (DACs) which create analog signalsto drive the red, green and blue channels of color display 570.

Variations of the Invention

Although the invention is described above as a system for themanipulation and display of MR data, it is also suitable for use withany digital image.

The concept of `smuggling` information into the lower bits can beapplied to any digitally encoded data.

The best use would be for merging additional information from a seconddata set into the primary data set which has entries that correspond tothe primary data set. As mentioned above, two volumetric data sets withentries representing two different physical characteristics at the samelocation could easily be combined. Merging these two data sets reducesthe amount of redundant information.

In other embodiments, text, voice, or sounds in general may be`smuggled` into an image to which they pertain without affecting imagequality. This allows a description of an image or video clip to beembedded within the image or video clip itself. It provides integralmulti-media. Enhanced media of this form are fully compatible with oldermedia players not capable of reading the embedded information.

In still another embodiment, small programs, or applets may be`smuggled` in a primary data set, such as an image. These applets maythen be executed, even on the image itself.

In yet another embodiment, supplementary information may be incorporatedinto digital audio data with minor detriment to sound quality (chosen tobe below the level of audible detection).

FIG. 9 shows a generalized version of an embodiment of the presentinvention. Much is as described for FIG. 8 above. Since both datasources for FIG. 8 involved digital image playback, some elements sharedin FIG. 8 are split up for the embodiment shown in FIG. 9.

As before, there are a primary data source 503 and a secondary datasource 551. Data from both sources are merged into the enhanced data andstored in storage device 850.

A primary playback device 861 is coupled to the storage device and couldplay back the enhanced data as if it were unaltered primary data.

A control device 855 coupled to the storage device 850 reads the lowestM bits and passes them to a secondary playback device 860 allowingplayback device 860 to reproduce the original information captured inthe secondary data set. Secondary playback device 860 may be a displaydevice, as show in FIG. 8, an audio playback device, a text andsuperposition device to superimpose textual description on images orvideo, or any other digital playback device. Secondary playback device860 is controlled by a user interface 880 which causes the secondaryplayback device to change one or more aspects of the secondary dataoutput such as volume, data format or the like.

While several presently preferred embodiments of the novel inventionhave been described in detail herein, many modifications and variationswill now become apparent to those skilled in the art. It is, therefore,to be understood that the appended claims are intended to cover all suchmodifications and variations as fall within the true spirit of theinvention.

What we claim is:
 1. A method of merging secondary data set informationinto a primary data set without destroying data or reducing a desireddynamic range comprising the steps of:a) acquiring primary data sethaving a plurality of data words; b) acquiring a secondary data sethaving data words which correspond to entries of the primary data set;c) reducing the secondary data words to M bits creating a reducedsecondary data word; d) determining a number of bits D for a maximumdesired dynamic range on playback; e) determining a number of bits P ina word of a playback device; f) merging M bits of reduced secondary dataword into M least significant bit positions of the primary data words toresult in enhanced data words.
 2. The method of merging of claim 1further comprising, before the step of merging, the step of:shifting theprimary data set words by a number of bit places F equal P-D.
 3. Themethod of merging of claim 1 wherein the primary data set comprises adigital image.
 4. The method of merging of claim 1 wherein the primarydata set comprises a magnetic resonance image.
 5. A system for merginginformation of a secondary data set from a secondary data source intounused portions of a primary data set from a primary data source withsubstantially no reduction in dynamic range and signal qualitycomprising:a) a storage device capable of storing digital information;b) a data reduction device coupled to the secondary data source forreducing secondary data words into shorter reduced secondary data words;c) a merge device coupled to the data reduction device for receiving thereduced secondary data words and incorporating these into the leastsignificant bits of the primary data words and storing them in thestorage device as enhanced data words.
 6. The system of claim 5 whereinthe data reduction device operates to determine a number of bits D for amaximum desired dynamic range on playback, determine a number of bits Pin a word of a playback device, pass the values of D and P to the mergedevice, reduce the secondary data words to a length of M bits, andproviding the reduced secondary data words to merge device.
 7. Thesystem of claim 6 wherein the merge device operates to shift a pluralityof primary data set words toward the most significant bit by a maximumnumber of bit places F equal to P-D, then merges M bits into M leastsignificant bit positions of the shifted primary data set words toresult in enhanced data set words retaining the desired dynamic range,and stores the enhanced data words in storage device.
 8. A method forenhancing primary data set words with secondary data set wordscomprising the steps of:a) reducing each of said secondary data setwords to M bits of data resulting in reduced data words; b) insertingthe reduced data words into the said primary data words.
 9. The methodof claim 8 further comprising the step of shifting the said primary datawords toward more significant bit positions by M bits, prior to theinsertion of the M reduced data bits to preserve all the bits of theprimary and secondary data words.
 10. The method of claim 8 furthercomprising the step of replacing the M leastmost significant bits of thesaid primary data words with the M reduced data bits to preserve thedynamic range of the bits of the primary and secondary data words. 11.The method of claim 8 wherein the secondary data set is velocity datafrom a phase-contrast magnetic resonance image.
 12. The method of claim8 wherein the secondary data set is difference data obtained bycomputing the difference between a reference data set and a subsequentdata set.